1. Field of the Invention
The present disclosure relates to a headlamp of a vehicle such as an automobile or the like and, in particular, it relates to a vehicle headlamp capable of being switched to multiple different light distribution patterns.
2. Related Art
A headlamp of an automobile or the like is designed to be able to switch a light distribution pattern in accordance with a traveling state and is generally designed to be able to be switched to “low beam” and a “high beam.” The “low beam” (also referred to as “passing beam”) preferably constitutes a light distribution pattern which does not distract the driver of a vehicle traveling in an opposite lane or a vehicle traveling ahead in the same direction. The “high beam” (also referred to as “running beam”) preferably constitutes a light distribution pattern for illuminating a wide range on a front side. In recent years, there also has been proposed a vehicle headlamp capable of being switched to a “middle beam” (also referred to as “motorway beam” or “remote optically recognizing beam”) constituting a light distribution pattern for illuminating a range of the front side as wide as possible so as not to distract the driver of a vehicle traveling in an opposite lane. As shown by FIG. 10A, a “low beam” light distribution pattern is constituted by a light distribution pattern for illuminating a lower side region constituting a cut line CL by a position of an angle of 0.57° slightly lower than a horizontal line (hereinafter, simply referred to as a light distribution horizontal line) H on the light distribution pattern at a region on a right side of a vertical line (hereinafter, simply referred to as light distribution vertical line) V constituting a reference by an optical axis of a headlamp and constituting a cut line CL by a height of the light distribution horizontal line H on a left side region. As shown by FIG. 10C, a “high beam” light distribution pattern is constituted by a light distribution pattern for illuminating a region having a cut line CL slightly on an upper side of the light distribution horizontal line H on left and right sides of the light distribution vertical line V, and at a position of an angle of 2° on an upper side of the light distribution horizontal line H particularly on a left side region. As shown by FIG. 10B, a “middle beam” light distribution pattern is constituted by a light distribution pattern for illuminating a lower side region constituting a cut line CL by a position of an angle of 0.23° slightly on a lower side of the light distribution horizontal line H on a right side region of the light distribution vertical line V and constituting a cut line CL by a position of an angle of 0.34° slightly on an upper side of the light distribution horizontal line H on a left side region. In the respective diagrams, a broken line indicates a light distribution region when light is not blocked by a shade, and a luminance intensity becomes high toward the center as indicated by outline equi-luminous intensity lines in the light distribution patterns of the respective diagrams.
A known headlamp capable of switching the light distribution patterns has a shade for partially blocking light emitted from a light source inside the headlamp and changing a pattern of light emitted from the headlamp by changing a position of the shade. For example, Japanese paten document JP-A-2005-259549 discloses a headlamp for switching a light distribution pattern by switching a shade for blocking light by providing a rotatable rotary shade as in a hydraulic turbine radially arranged with multiple shades having different shapes at a position on a front side of a light source and switching the shades for blocking light by controlling a position of rotating the rotary shade.
According to the headlamp of JP-A-2005-259549, a desired light distribution pattern is provided by changing the illuminating range by blocking a portion of light of a constant light distribution pattern emitted from the light source by the rotary shade. In other words, the respective light distribution patterns are formed by cutting out portions of the light distribution pattern emitted from the light source. As shown by FIG. 10B, according to the “middle beam” light distribution pattern, a region along the light distribution horizontal line H is blocked. Thus, in the “middle beam” light distribution pattern, a region having a high luminous intensity at a vicinity of the optical axis of the headlamp of a moving vehicle is blocked, and a luminous intensity of a remote region ahead of the vehicle becomes low. Therefore, a problem can arise because insufficient remote optical illumination is achieved in the “middle beam” light distribution pattern According to the headlamp of JP-A-2005-259549, a state occurs in which illumination is dark by temporarily switching to a state of “low beam” as a result of a relationship of aligning the shades of the rotary shade, when switched from “middle beam” to “high beam.” Such a state may adversely affect the driver. This is because the rotary shade of the headlamp of JP-A-2005-259549 switches the shades by being rotated reciprocally and, when the different light distribution patterns are switched, a light distribution pattern occurs other than the desired light distribution pattern over time. This also poses a difficulty in switching to a desired light distribution pattern when traveling at high speed.